1. Field of Invention
The present invention relates to a swash plate of a swash-plate compressor, more particularly to surface-treatment technique for improving the sliding characteristics of the swash plate consisting of iron or aluminum-based material.
2. Description of Related Art
A swash-plate type compressor is shown, for example in U.S. Pat. No. 5,228,379 (c.f., FIG. 3). In a swash-plate type compressor, a swash plate 4 shown in FIG. 1 is rigidly secured obliquely to a rotary shaft (not shown) in such a manner that its slanting angle is variable. The swash plate 14 is engaged via the front shoes (not shown) and the rear shoes 19 with the piston (not shown). The descriptions of U.S. Pat. No. 5,228,379 (column 3, lines 16-48 are incorporated herein for describing the parts shown in FIG. 1.
The refrigerant gas is sucked from the suction chamber into the cylinder bores and is then compressed. The compressed refrigerant gas is discharged into the discharging chamber.
A noteworthy point in the sliding conditions of a swash-plate is that, during the initial operational period of a compressor, the refrigerant gas reaches the sliding part prior to the lubricating oil reaching the sliding part between the swash plate 14 and the shoes 19; thus the refrigerant gas has a rinsing effect on the lubricating oil which remains on the sliding part, with the result that the sliding condition is in a dry condition free of the lubricating oil. Seizure is, therefore, very likely to occur.
A number of the surface-treatment methods have, therefore, been proposed to adapt a swash plate to the sliding conditions as described above. The flame spraying of copper is recently proposed in domestic publication of PCT application WO95/25224 and Japanese Unexamined Patent Publication (kokai) No. 8-331,634.
Meanwhile, an academic paper entitled "Friction Wear Characteristics of Solid-Lubricant Coating in Coexistent Condition of Refrigerant and Lubrication Oil of Freezing Machine" was published in a solid-lubricant research meeting of Japanese Society for Tribology. According to this publication, the solid-lubricant coating, in which polyamide-imide is used as the binder, is tested under the conditions of non-lubrication and refrigerant gas. The solid-lubricant coating exhibits the best performance when MoS.sub.2, Sb.sub.2 O.sub.3 and graphite are added together. The solid-lubricant coating exhibits a slightly inferior performance, when only MoS.sub.2 is added. The coating with only the binder and without the solid lubricant exhibits the worst performance. The substrate material, on which the solid-lubricant coating is applied, is chromated hyper-eutectic Al--Si alloy.